An interposer is used as a substrate that electrically connects a semiconductor element to a mounting substrate such as a motherboard. For example, a through electrode is formed in the interposer to electrically connect wires arranged in the upper and lower surfaces of a silicon substrate.
A typical method for forming the through electrode will now be described. First, a through hole is formed in a silicon substrate. Then, the silicon substrate is thermally oxidized to form an insulation film on the upper and lower surfaces of the silicon substrate and the wall surface of the through hole. A metal foil is adhered to the lower surface of the silicon substrate and the wall surface of the through hole. Then, electrolytic plating is performed using the metal foil as a power supplying layer so that a plating film (e.g., copper layer) is deposited and grown from the metal foil to fill the through hole with the plating film. Subsequently, the plating film that projects upward from the upper surface of the silicon substrate is polished by performing chemical mechanical polishing (CMP) to form the through electrode. Japanese Laid-Open Patent Publication No. 2005-11987 describes a method for forming such a through electrode. In this manner, the through electrode is formed using a bottom-up plating technique.
In the above method, the entire through hole is filled with the plating film. Thus, the formation of the through electrode takes time.